Tropical cyclone Seroja’s aftermath: Flash flood inundation modeling and recovery efforts in rural coastal Lembata, East Nusa Tenggara Province, Indonesia

As the risk of adverse impacts from tropical cyclones increases globally, more people and assets are being exposed to the potential damage they may cause. However, not much is known about the processes of flash floods triggered by tropical cyclones, evacuation, and post-disaster recovery, particularly in Indonesia's coastal regions. This study focuses on the coastal village of Wowong, located in Lembata Island, East Nusa Tenggara Province, which was affected by flash floods caused by the 2021 Tropical Cyclone Seroja. The objectives are: (1) to simulate flash floods based on extreme rainfall conditions during the cyclone and (2) to analyze the post-disaster recovery conditions following the flash floods. The method used to simulate flash floods is unsteady flow through the HEC-RAS hydraulic model, while post-disaster recovery analysis is conducted through focus group discussions and household surveys of flood-affected communities. The simulation shows that almost the entire village of Wowong was inundated with floodwaters, with a maximum depth reaching 3 meters. The flood model was validated through statistical tests, producing a Kendall-Tau correlation coefficient of 0.59 (p = 2.2e-08). The sectors investigated for their recovery levels include water and sanitation, housing and infrastructure, livelihoods, as well as education and health. Recovery mechanisms largely stem from community self-help organizations, which are considered an uninstitutionalized social capital, as well as support from the government and non-governmental organizations. This study can serve as a consideration for local governments in prioritizing development and integrating social networks in areas affected by flash floods to prepare for disaster anticipatory action.